SNIP: A Sensor Node-Initiated Probing mechanism for opportunistic data collection in sparse wireless sensor networks

In many potential wireless sensor network applications, the cost of the base station infrastructure can be prohibitive. Instead, we consider the opportunistic use of mobile devices carried by people in daily life to collect sensor data. As the movement of these mobile nodes is by definition uncontrolled, contact probing is a challenging task, particularly for sensor nodes which need to be duty-cycled to achieve long life. We propose a Sensor Node-Initiated Probing mechanism for improving the contact capacity when the duty cycle of a sensor node is fixed. In contrast to existing mobile node-initiated probing mechanisms, in which the mobile node broadcasts a beacon periodically, in SNIP the sensor node broadcasts a beacon each time its radio is turned on according to its duty cycle. We study SNIP through both analysis and network simulation. The evaluation results indicate that SNIP performs much better than mobile-initiated probing. When the fixed duty cycle is lower than 1%, the probed contact capacity can be increased by an order of 2-10; alternatively, SNIP can achieve the same amount of probed contact capacity with much less energy consumption.